A Risk Comparison between Lifestyle, Socioeconomic Status, and Radiation: A Cohort Study of Cancer Mortality among Japanese Nuclear Workers (J-EPISODE)

The health effects of low-dose radiation exposure have been a source of controversy. One possible reason is that epidemiological studies that compare radiation risk with other factors, such as lifestyle or socioeconomic status, have been limited. The aim of this study is to conduct a comparison of the cancer risk of mortality between radiation, lifestyle habits (such as smoking), and socioeconomic status (such as years of education) among Japanese nuclear workers. We assembled a cohort of 41,742 male nuclear workers in Japan who answered a lifestyle questionnaire survey conducted during 2003-2004. To exclude systematic errors caused by missing values, we used multiple imputation and Poisson regression to estimate relative risks and confidence intervals for lifestyle habits, socioeconomic status, and radiation. The total person-y from 2005 to 2010 were 215,000. The mean age and cumulative dose were 54.9 y and 24.8 mSv (10-y lagged dose), respectively. Significantly high relative risks were determined for smoking, alcohol consumption, frequency of medical examination, breakfast intake, sleep, and body mass index. Further, significantly high relative risks of radiation were shown for lung cancer and smoking-related cancers. Since the simultaneous inclusion of radiation and non-radiation variables in the model for relative risk (RR) calculation means that the calculated radiation RR is the result of adjustment by other variables, the risk of cancer from low-dose radiation, if any, is less than smoking and probably less than other lifestyle factors.